Social Networks want to be found, so they make some information – most notably, profiles – public, visible to search engines. At the same time, they want members to join and sometimes pay for the search. They also worry about their members’ data privacy. It is a balance for each site – which pages and how much info to let Google find. It is not uncommon for a social site to decide to hide previously visible public info.
So the Surface Web is not only expanding but shrinking too!
Meetup.com has recently “lost” public profiles. Github.com used to have